1. Field of the Invention
This invention relates to an automatic shut off device for an apparatus for melting powdered sulfur.
2. Background
United States patent application Ser. No. 236,560, filed of even date herewith is directed to an apparatus for melting powdered sulfur, particularly an on-site batch-type unit that finds use producing molten sulfur for incorporation into sulfur-based coatings and the like. The apparatus of that application has an expanded surface area sloping bottom and preferably employs combustion heating. As pointed out in that application, the melting of powdered sulfur is more difficult than might be expected because of the tendency of the material to form "bridges" away from the heating elements and its flamability when overheated.
The melter of that application is generally operated on a batch basis. In such a mode of operation, it is required to shut down the heat to the melter when the batch charge is melted and removed. Usual ways of effecting such control include (1) having a mechanical arm-like device that measures the top level of the solid sulfur load or (2) having a mechanical load-bearing weighing device mounted on the bottom of the box. Both of these devices would turn off the heat when the measuring mechanism has moved a predetermined distance. In a molten vaporous sulfur environment, use of such devices is not feasible because of jamming and corrosion problems. Additionally, such devices would not detect a bridge or jam which prevented solid sulfur present in the melter hopper from reaching the melting plate. A failure to promptly shut down the heat either when the load is exhausted or when bridging has occurred, could lead to overheating and fires.